The present invention relates to a drilling device for producing drill holes with undercuts and particularly to such a device which has a drill with a drill shaft with projecting drilling plates, and a shoulder extending from the drill shaft.
Drilling devices of the above mentioned general type are known in the art. They are used for forming an undercut at the bottom of the drill hole by turning the drill, in order to insure form-locking anchoring of an expansion plug in the drill hole. The expansion plug inserted in the drill hole engages in the undercut with its expansion part.
The German document No. DE-OS 2,349,998 discloses a which a ball-shaped shoulder is arranged in the drill shaft and serves as a bearing for turning. The collar can abut during turning against a mouth of the drill hole for forming the bearing. In this known drilling device it is possible that the drilling material which is produced during the drilling process cannot be sufficiently evacuated outwardly from the drill hole. Moreover, the turning region is not limited, so that it will not match in an optimal manner an expansion plug to be inserted.